Regulation of intracellular pH in proximal tubules of avian loopless reptilian-type nephrons

In proximal tubules isolated from chicken superficial loopless reptilian-type nephrons, intracellular pH (pH(i)), measured with pH-sensitive fluorescent dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein, was similar to 7.1-7.2 under control conditions (N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered medium with pH 7.4 at 37 degrees C), and was reduced to similar to 6.9 in response to NH4Cl pulse. The rate of recovery of pH(i) (control value congruent to 5 x 10(-3) pH U/s) from this acid level was I) significantly decreased by removal of Na+ or both Na+ and Cl- from the bath or addition of 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (0.25 mM) to the bath, 2) significantly increased by high bath K+ (75 mM), and 3) unchanged by removal of Cl- alone from the bath or addition of ethylisopropylamiloride (1 mM) or Ba2+ (5 mM) to the bath. Resting pH(i) was 1) significantly decreased by Na+ or simultaneous Na+ and Cl- removal, 2) significantly increased by high K+, and 3) unchanged by Cl- removal alone or addition of Ba2+. The data do not fit the concept of pH(i) regulation by the most commonly suggested basolateral transporters (Na+/H+ exchanger, Na+-dependent and Na+-independent Cl-/HCO3- exchangers, or Na+-HCO3--CO32- cotransporter).